Granite is an acidic rock corresponding to rhyolite in chemical composition.
Surface eruption of quartz-porphyry, rhyolite, and andesite.
This is shown in the glaciated rock-surfaces of the rim that are covered with layers of pumice and rhyolite.
After making a most thorough examination my opinion is Southern part Ely Central property is covered by rhyolite capping.
In the south of the island there are sills and dykes of felsite, quartz-porphyry, rhyolite, trachyte and pitchstone.
The oldest volcanic rock appears to be rhyolite, which peers up in two small hills almost smothered beneath the lake deposits.
The northwest corner is volcanic and is made up of rhyolite, obsidian, and lava.
Basalt is less siliceous than granite and rhyolite, and contains much more iron, calcium, and magnesium.
There is no question that the rhyolite was deposited in Ely Central after the enrichment of the porphyry.
rhyolite and other forms of lava were last spread over the region.